In treatment of tumors and cancerous tissues in human body, various methods are available, which include medication, radiation, dissection and ablation. Radio frequency (RF) ablation is commonly used to treat diseased tissues. RF ablation is a tissue treatment by which two or more electrodes are inserted into the vicinity of a diseased tissue and an alternating electrical current, typically at a frequency of a few hundred kHz, is applied to the tissue through the electrodes to ablate the tissue between the two electrodes. It is commonly believed that when the RF current passes through the tissue, electrical energy transforms into heat by what is known as Joule heating effect, and when the temperature of the tissue is high enough (it is generally believed that the temperature needs to be above 55° C.), the cells of the tissue between the two electrodes are destroyed. For most tissue ablation cases, it is desirable to ablate the tissues only within intended boundaries (e.g., desirable size and shape). Therefore, it is critical that the RF energy is directed only to the targeted tissue within the desirable boundaries to minimize damage to the healthy tissues surrounding the targeted tissue.
“Le Veen Needle Electrodes”, described by U.S. Pat. No. 5,868,740, is a device currently available on the market for the treatment of tumors and cancerous tissues. This device contains an array of deployable needles, which can be inserted into the tumor tissue, and a large grounding pad, which may be in contact with a large area of the skin of a patient. In an ablation operation, the needles are inserted into the diseased tissue and the ground pad is properly placed in contact with a large area of the skin of the patient. Then, an RF current is applied to all the needle electrodes at once. The current passes through the diseased tissue (and some normal tissues) at higher current density, the large area of skin at lower current density, and the grounding pad, going back to the RF power source. This technique is referred to as monopolar RF ablation technology. The drawback of the technique is that because the RF current goes through part of the healthy tissues, it sometimes causes unintended damages to them if the current is not carefully controlled.
In U.S. Pat. No. 5,693,078, Jawahar Desai discloses a device and technique for generating a large lesion to treat endocardiac tissue for ventricular tachycardia and other cardiac dysrhythmias. Desai used an array of electrodes, which was placed on the surface of the ablation zone and an RF power source that had a plurality of voltage outputs, each having an individual phase. Each individual electrode was connected to one of the individually phased outputs of the RF power source. When power was turned on, the electrode array together with the multi-phased RF power source produced plural current paths on the surface of the ablation zone and resulted in a uniform lesion with a size defined by the span of the electrode array. This method is good in the sense that it can generate a bigger lesion on the surface of a targeted area. However, it does not provide any means for controlling the depth of ablation; and the RF electrical current tends to concentrate in the vicinity of the needles. Therefore, this device cannot be used to achieve desirable three-dimensional large lesions consistently.
U.S. Pat. No. 6,514,252 disclosed a device for ablating tissue using two optional arrays of tissue penetration elements (needles) on a pair of actuable jaws using bipolar RF energy. This device extended the electrodes from the forceps to the tip of the needles. However, the application of this device is not really suitable for tumors or other type of tissues due to the fact that it is attached to a jaw mechanism.
For all the reasons mentioned above, there is a need for developing a device, which is capable of producing large and uniform three-dimensional lesions by using bipolar RF energy; and there is a need for developing a method capable of controlling the size and shape of three-dimensional lesions by using bipolar RF energy.